Preheat oven to 400°F (200°C). Grease an 8-in. (20 cm) baking dish. Heat oil in a large skillet over medium-high heat. Add beef, red pepper, onion, cumin and cayenne, if using, and cook, using a fork to break up meat, until meat is no longer pink and vegetables are tender, about 5 min. Drain any liquid then stir in 1/2 cup (125 mL) cheese, half the chipotle sauce and 3 tbsp (45 mL) cilantro.
Evenly scoop mixture into centre of each tortilla. Fold sides over filling, then roll to enclose filling completely. Place enchiladas, seam side down, in prepared baking dish. Spread remaining chipotle sauce overtop and sprinkle with remaining cheese. Bake on middle rack of oven until cheese is melted and bubbly, about 10 min. Garnish with remaining cilantro.
To turn up the heat, add a pinch of cayenne pepper.