Cut peppers in half lengthwise and clean out. Place in foil-lined large glass dish and lightly spray with olive oil. Cover with foil and bake for 20 minutes.
Meanwhile, heat some oil in Dutch oven over med-high heat. Add onion (save 1 tsp. minced onion for Greek yogurt), garlic, salt, pepper, chili powder, and cumin until onion gets soft (about 3-5 minutes).
Add turkey to onions breaking it up as it browns (about 5 minutes). Add salsa and half of spinach. Let spinach wilt and add second half.
Remove from heat and stir in cooked rice.
Carefully fill peppers, cover with foil, and bake 20-25 minutes.
Prepare Greek yogurt by adding reserved minced onion and lemon juice.
Remove foil, sprinkle with cheese, and bake another 5-7 minutes uncovered.
Serve with avocado slices and a dollop of Greek yogurt.
Notes
If you like your food spicy, consider adding more chili powder. Also, buy medium or hot salsa.