Chop the onion and garlic into relatively small dice. Optionally peel the tomatoes, but either way, chop relatively small. Cut the zucchini/courgette in half then into slices, cutting larger half-slices in half again. Try to make the slices relatively even to help them cook evenly. Remove seeds and stem from poblano pepper and dice.
Warm the oil in a medium skillet/frying pan over a medium-high heat. Add onion and poblano pepper and cook for around 5 minutes until both (but most obviously the onion) are softening. You don't want them to burn, so reduce the heat or add a little extra oil if needed. Add the garlic and zucchini/courgette, stir and cook briefly, then add the tomato, oregano, cumin, salt and pepper. Mix through then cover the skillet with a lid and reduce the heat a little as needed. Allow to cook, stirring gently now and then, until the zucchini is becoming tender.
Add the garlic and zucchini/courgette, stir and cook a minute or two, then add the tomato, oregano, cumin, salt and pepper. Mix through then cover the skillet with a lid and reduce the heat a little as needed so it gently simmers. Allow to cook, stirring gently now and then, until the zucchini is becoming tender - it should change color a little but not become mushy. You want it to still have a bit of bite. The tomato should soften to give a bit of liquid but if needed, add a tablespoon or two water to help stay moist.
Add the corn, mix through then cover and cook a minute more, or a couple minutes if it's fresh corn.
Add the cheese and optionally mix through (if you mix it in, you often get slight clumps here and there but it feels more vegetable-y overall, if you leave on top you get a cheesy layer on top then al the vegetables underneath. I mixed in a little in photos). Cover, remove from heat and allow cheese to melt then serve, optionally with some cotija cheese sprinkled on top.