Tekkaman doesn’t have a fast or reliable AA move, so most of the time you just want to sit tight and react to the opponent and block correctly or throw tech. Look for small breaks during their block strings, and insert assist during them, sometimes using advance guard first. If the person likes to jump a lot, air throw them (one of the best options). You can also jump back with j.A or j.B and then jump cancel that and go for the ambiguous crossup, empty jump to throw, tick throw, etc. At the very least you’ll get a chance to turn the pressure back on them. And if there is enough time, you can even advance guard and use C ~ Tek Lancer. It often intercepts people abusing too much IAD, and leads to an easy Voltekka on reaction.
Regarding Zero, if you’re letting him get that close too often, you’re not zoning him well enough. Tekkaman isn’t a character you can just rush out of nowhere. All of his air moves control great amounts of space and can make it very hard to approach him when used right. All I can say here is study the Zero player and see what he likes to do often. All air moves can stop far IADs. j.A, j.B, and air throws stop them from up close. j.B stops people from above that want to stay out of j.A’s range. Galaxy Windmill will stop excessive use of C ~ Hienkyaku shenanigans.
Zero’s damage output is a big disadvantage here considering Tekkaman’s high HP, but with the right setups, Tekkaman only has to touch him once and it’s over if Zero doesn’t have 2 bars. It should be Zero running away from him, not the other way around.