Tentai Senshi Sunred

Much like Saitama, Sunred is a hero who's lost his passion. Monsters are too easy to defeat, and his life has become a dull routine. However, Sunred's relationship with monsters is a bit more amicable than Saitama's. General Vamp - leader of the Florsheim Monsters - is more like Sunred's affable arch-frenemy, frequently showing up at his house just to hang out. The show largely about the day-to-day slice-of-life downtime between heroes and villains. If you like OPM's sense of humor, you might like Sunred's as well. 

The main character is a lazy guy who unexpectedly turns out to be a superhero tasked with protecting their city against weird monsters. Both are comedies, although One Punch Man is more action-focused than Tentai Senshi Sunred, which moreso feels like a pure slice of life. Also, Tentai Senshi Sunred has very minimalistic animation whereas One Punch Man is a big-budget kind of thing. But they have the same kind of charm once you see past that. 

Both are superhero parody anime with OP main character and comedic villains. So far One Punch Man's jokes are a little on the repetitive side while Sunred has a more diverse type of jokes. Personally I think Sunred is funnier but if you like one you'll like the other. 

Super-hero parody. OP MC, with a bland and funny head (bald derp/helmet), bored and annoyed about his opponents, who are creepy and bragging, struggling in his mundane life, somewhat a loser (shut-in/pachinko). Becomes more serious near the end. Sometimes, animation quality is used as a gag (drop for Saitama/Tatsumaki moe-blobs/sakuga). The aesthetic is more comics and manga in OPM, while tokusatsu in Sunred. There is a twist with polite villains vs. rude hero in Sunred, as opposed to exaggerated clichéed characters in OPM. The jokes are more diverse, less repetitive and predictable in Sunred. The animation quality in OPM is way better, but Sunred's art-style serves it better. 

Both anime revolve around an OP hero fighting off puny villains who look somehow similarly creepy.Both have comedy, parody and super power as their genre.  

Superhero parodies with overpowered protagonists. TSS is a much better anime in total, with great characters and extremely funny comedy. If you liked OPM you should really trust me on this; do not allow yourself to be deterred from the shitty animation and watch TSS. 

both are tokusatsu-inspired with laid-back atmosphere tentai senshi has more gag humors  

Slice of life shows about managing evil monster organizations as they battle against local heroes. Kaijin Kaihatsu-bu was definitely influenced by Sunred, in fact, the whole gang makes an appearance in episode 11 starting at 7:05 

Funny fighting and aliens. Short episodes. Random humor and weirdly wholesome characters. 

Both shows have a similar type of humour and has a similar feel to it and a similar type of comedic approach, while Gintama parodies a broad range of anime, Tentai Senshi Sunred only parodies the "Super Sentai" genre i.e stuff like Power Rangers. 

If you like your anime with a slice of comedy, look no further. Either that or you want to see a hero's day off.