Slice the bell peppers into thin strips and thinly slice the onion. Prepare the zucchini by slicing into half-moons for even cooking.
Heat your cast iron skillet over medium-high heat until hot and shimmering. Add a tablespoon of olive oil and let it coat the pan evenly.
Add the sliced onions and peppers to the hot skillet. Spread them out so they make contact with the surface and begin to sizzle. Cook for about 8 minutes, stirring occasionally, until they develop charred edges and soften.
When the vegetables are starting to char and smell sweet and smoky, sprinkle the cumin and smoked paprika over them. Toss everything to coat evenly and cook for another 2-3 minutes until fragrant.
Stir in the sliced zucchini and cook for another 3 minutes, until the zucchini is tender but still holds its shape and has a slight caramelization.
Squeeze the juice of a lime over the vegetables, tossing gently to evenly distribute the bright, tangy flavor. Remove from heat and let sit for a minute.
Warm the tortillas in a dry skillet or microwave until soft and pliable, about 15 seconds.
Fill each tortilla with the smoky, caramelized vegetables. Serve immediately while warm, garnished with extra lime or fresh herbs if desired.
