Combine spices, salt, and pepper in a small bowl. Mix oil and lime juice in a measuring cup, then whisk in the spice mixture until well combined.
Place chicken thighs in a sealable plastic bag, add marinade, and seal, removing excess air. Refrigerate for 45 minutes, flipping halfway through. Remove from fridge 15 minutes before grilling.
Preheat grill to 375°F. Grill chicken for 5 minutes on first side, flip and cook 3 minutes on second side. Continue cooking until internal temperature reaches 165°F. Let rest 5 minutes before chopping.
Divide rice among four bowls (1 cup each). Top each with chopped chicken, ¼ cup black beans, ¼ cup pico de gallo, 2 tbsp cheese, and 1-2 tbsp guacamole. Garnish with cilantro if desired.