Peel chayote, trim ends, and halve lengthwise. Use a spoon to scoop seed out of each half. Cut into ¼" dice. Halve and peel onion. Cut halves into ¼" dice. Stem poblano pepper, seed, and cut into ¼" dice. Mince cilantro (no need to stem).

Heat 2 tsp. olive oil in a medium non-stick pan over medium-high heat. Place chayote in hot pan and cook undisturbed until lightly browned, 2-3 minutes.

Add onion, poblano (to taste), corn, and cilantro (reserve a pinch for garnish) to pan. Cook, stirring occasionally, until vegetables are tender, 4-5 minutes. Remove pan from burner and allow filling to cool at least 5 minutes. Once filling has cooled, stir in ¼ the cheese (reserve remaining to top enchiladas). Season with ½ tsp. salt and a pinch of pepper.

Pour ⅓ cup enchilada sauce into prepared casserole dish (use a dish large enough to fit six rolled tortillas), coating the bottom. Place one tortilla on a clean cutting board. Add ⅓ cup filling to tortilla, tightly roll up, and place in casserole dish, seam-side down. Repeat for remaining five tortillas. Don't overfill tortillas. Make sure ends overlap and have a chance to seal while baking. Top with remaining enchilada sauce. Place any remaining filling in casserole dish and top enchiladas with remaining cheese.

Spray a piece of foil with cooking spray and place over casserole dish, sprayed side down. Tightly seal foil and bake 12-15 minutes. Remove foil and bake until cheese is bubbly, 7 minutes.

Place three enchiladas on a plate. Ladle any remaining sauce from casserole dish on plate with enchiladas. Garnish with remaining cilantro.