Place sliced onions in an even layer in the bottom of the slow cooker, then add the chicken breasts.
2 pounds boneless skinless chicken breasts, 1 yellow onion
In a medium bowl or liquid measuring cup, stir together the diced tomatoes, lime juice, minced garlic, chili powder, cumin, paprika, sugar, salt and pepper. Pour the mixture over the chicken breasts in the crockpot.
10 ounce can petite diced tomatoes with jalapeño and cilantro, 2 tablespoons fresh lime juice, 2 cloves garlic, 2 teaspoons chili powder, 1 teaspoon ground cumin, 1 teaspoon paprika, 1 teaspoon granulated sugar, ½ teaspoon salt, ¼ teaspoon black pepper
Option 1: For softer peppers (or convenience if you'll be away from the kitchen until dinner time), add the bell peppers on top of the chicken.Option 2: For firmer bell peppers, wait and add them to the slow cooker when there is one hour of cook time left. (Or 1.5-2 hours left if cooking on low.) Add them quickly so as to minimize the time with the lid off the crockpot - you don't want too much heat to escape. 1 red bell pepper, 1 yellow bell pepper
Cover and cook on low for 3-5 hours or high for 2-3 hours, or until chicken is cooked through and shreds easily with a fork. Chicken should register at least 165° F on an instant-read thermometer inserted into the thickest part of the chicken.
Remove chicken from crock pot and let rest for 5 minutes. While it rests, remove and discard about 1 cup of the liquid in the crockpot (I use a spoon or quarter cup measuring cup to do this.) Then shred chicken and return it to the crock pot.
Optional: Briefly char the tortillas in a hot skillet on the stove. Serve chicken, bell peppers and onions in tortillas, with toppings as desired.
12 small flour tortillas, sliced avocado, chopped fresh cilantro, sour cream or plain Greek yogurt