Step 1: Prep the Chicken: Pat chicken dry. In a bowl, toss chicken with olive oil, chipotle powder, cumin, paprika, garlic powder, salt, and pepper until coated.
Step 2: Grill Chicken: Grill chicken on a grill or grill pan over medium-high heat for 5-7 minutes per side until cooked through (internal temp 165°F). Rest chicken on a cutting board for a few minutes, then dice or shred.
Step 3: Make Chipotle Ranch Dressing: In a medium bowl, whisk together mayonnaise, buttermilk, sour cream (or yogurt), lime juice, minced chipotles, adobo sauce, garlic powder, onion powder, dried dill, salt, and pepper until smooth. Adjust seasoning/heat to taste.
Step 4: Warm Tortillas: Warm tortillas according to package directions until pliable (microwave, dry skillet, or oven).
Step 5: Assemble Burritos: Lay a warm tortilla flat. Spread a generous amount of chipotle ranch dressing down the center.
Step 6: Layer Fillings: Pile on cooked rice, black beans, grilled chicken, shredded cheese, diced tomatoes, and shredded lettuce. Add optional red onion, cilantro, or avocado.
Step 7: Roll Burritos: Fold in the sides of the tortilla. Grab the bottom edge and tightly roll it up over the fillings, tucking everything in as you go, until you have a secure burrito.
Step 8: Serve: Serve immediately, with extra chipotle ranch dressing on the side for dipping if desired.