
Blend the tomatoes, 2 chipotle peppers plus 1 tablespoon of their sauce, garlic, oregano, and salt until smooth. Use just 1 chipotle for a milder, kid-friendly version.
Slice the onion into the slow cooker, set the chicken on top, and pour the sauce over.
Cover and cook on LOW for 4-5 hours (or HIGH for 2.5) until the chicken is tender.
Shred the chicken in the pot and stir it into the sauce. If it's watery, cook uncovered on HIGH for 15 minutes.
Warm the refried beans. Spread beans on each tostada, then top with chicken, lettuce, and cotija.
Photo: DinnerDrop