Gary Portnoy is not the most prolific television theme writer. He’s a singer-songwriter first who’s created TV themes as a sort of sideline. Maybe his best-known song is "Where Everybody Knows Your Name" that he wrote (with Judy Hart Angelo) and sang that was the theme song for the very-popular Cheers. He recorded a longer version of it that was released as a single. It reached #83 in the US and #58 in the UK.
He and Angelo also wrote the theme for Punky Brewster, which he also sang.
And the theme for Mr. Belvidere. Leon Redbone sang the theme for the show. Portnoy did a full version of the song on his 2007 album Destiny.
A partial list of the songs he’s written for other artists can be found of Wikipedia. Gary Portnoy, your Two For Tuesday, February 4, 2020.