In a large bowl, mix together the tomato paste, yogurt, paprika, red pepper flakes, cumin, black pepper, oregano, salt, garlic, and olive oil.
Add the chicken legs to the bowl one by one, coating each piece thoroughly with the marinade. Cover the bowl with plastic wrap and refrigerate for at least 1 hour, ideally 4–5 hours or overnight for deeper flavor.
Preheat your oven to 200°C (400°F) and line a baking sheet with parchment paper.
Arrange the marinated chicken legs skin side down on the prepared baking sheet, leaving space between each piece.
Bake in the center of the oven for 25 minutes. Then flip the chicken legs, place the tray on a lower rack (to prevent burning), and bake for another 15–20 minutes, or until nicely browned and cooked through.