3 tablespoons sweet chili sauce, plus more for serving
8 soft 6-inch flour tortillas
1 cup cilantro leaves & tender stems
Juice of 1 lime, plus lime wedges for serving
Combine 1 tablespoon of the oil, 1 tablespoon of the chili powder, ½ teaspoon each salt and pepper, garlic, and cayenne pepper in a bowl. Add the chicken and rub the oil mixture all over. Cover and marinate in the refrigerator for at least 1 hour and up to 12 hours.
Add another 2 tablespoons of oil to a large heavy skillet, heat to medium high, then add the chicken and cook, trying not to move, until golden and crisped, 5 minutes per side. Transfer to a plate and cover with foil to keep warm.
Heat the remaining tablespoon of oil in the skillet, then add the red and green bell peppers, onions, zucchini, and jalapeño to the skillet along with the remaining tablespoon of chili powder and ½ teaspoon each salt and pepper and cook, stirring, until the onions and peppers are partially charred and softened, 7 to 8 minutes. Slice the chicken into strips and add to the skillet along with any accumulated juices, the lime juice, and the sweet chili sauce. Warm through, 1 to 2 minutes. Season with more salt to taste.
Use tongs to carefully char the flour tortillas right on the stovetop over an open flame for about 10 seconds per side. Fill the tortillas with the filling, add some cilantro to each taco, and drizzle with sweet chili sauce. Serve tacos with more cilantro, chili sauce, and lime wedges.