Heat 2 tablespoons oil in a skillet over medium-high heat. Add onion and cook until golden brown, 5 to 7 minutes. Stir in mushrooms, bell peppers, and jalapenos. Season with salt, pepper, and chili powder. Cook and stir until vegetables are tender, 10 to 15 minutes.
Lightly brush tortillas with olive oil. Place tortillas on a grill or skillet over medium heat and heat until char marks start to appear, 1 to 2 minutes.
Divide mushroom and bell pepper mixture among tortillas. Top with Cheddar cheese and heat until cheese melts, about 2 minutes. Garnish with cilantro.