Preheat broiler to high.
Cut off top third of each bell pepper (keeping stem intact). Remove seeds and membranes from peppers. Set tops aside for later.
Arrange peppers on prepared baking sheet lined with parchment paper and coat with olive oil spray. Broil 4 minutes, turn the peppers over, then broil for 4 more minutes until peppers start to char.
When peppers are done broiling, set oven to 350°F.
In a large bowl, prepare the filling by combining the remaining ingredients.
Place broiled peppers in a deep baking dish, cut sides up, and stuff each pepper with 3/4 cup of the filling mixture. Top each pepper with 2 tablespoons tzatziki. Place reserved tops over top.
Bake for 10 minutes, then broil for 2 minutes to char the tops.