Preheat oven to 375 degrees. Oil or spray a deep square baking dish. Set aside.
Heat butter and oil in a saute pan over medium-high heat. Add the onion and cook for 4-5 minutes or until it begins to soften.
Add the sliced zucchini, yellow squash and chopped poblano peppers and continue cooking, stirring often another 5-6 minutes or until vegetables are starting to become tender.
Add the corn kernels and garlic and stir until garlic is fragrant, approximately 30 seconds. Transfer to the prepared baking dish to cool slightly, leaving behind any excess liquid.
While vegetables are cooling, whisk together cream cheese, mayonnaise, half and half and eggs.
Stir 1 1/2 cups of the cheese into the vegetables.
Pour the custard mixture over the vegetable and cheese mixture. Use a small spoon to nudge the vegetables aside in several places so the custard can trickle down and not pool on top.
Top with remaining cheese and tortilla chips.
Cover loosely with aluminum foil.
Bake 30-35 minutes. Remove foil and bake another 10-15 minutes or until cheese on the top is nicely melted and casserole is bubbling.
Sprinkle with a little chili powder to garnish.