Marinate the chicken: In a bowl, whisk olive oil, lime juice and zest, garlic, cumin, paprika, salt, and pepper. Add chicken breasts, coat well, cover, and refrigerate for at least 15 minutes (up to 2 hours). 2. While chicken marinates, slice bell peppers into 1/2-inch strips and red onion into 1/2-inch wedges. Toss with olive oil and salt. 3. Preheat grill or grill pan to medium-high heat (about 400°F). 4. Grill chicken 6-7 minutes per side, until internal temperature reaches 165°F and juices run clear. Let rest 5 minutes, then slice against the grain into strips. 5. Meanwhile, grill pepper strips and onion wedges 4-5 minutes per side, until charred and tender. 6. Warm tortillas on the grill for 30 seconds per side, or wrap in foil and warm in a 350°F oven for 5 minutes. 7. Arrange sliced chicken, grilled veggies, and all toppings in separate bowls. Let everyone build their own fajitas.