Preheat your oven to 350 degrees f. and grease a 13x9 baking dish with some cooking spray, or lightly brush with avocado oil.
Heat a large skillet over medium-high heat.
Add a tablespoon of oil and heat.
Carefully place your chicken into the hot oil, skin side down, and sear until nicely golden and brown, about 3 minutes on each side.
Transfer your chicken into the prepared baking dish and set aside.
Using the same heated skillet, add remaining tablespoon of oil.
Add in onions and sauté until tender. Stir in garlic and cook until fragrant, about 1 more minute.
Stir in your tomato sauce, vinegar, ground mustard, oregano, chili powder, and cinnamon.
Season with sea salt and pepper to taste, then whisk well and let it simmer on low for about 5 minutes stirring occasionally.
Stir in honey/maple syrup and cook for additional 2 minutes.
Pour this sauce over the chicken breasts and transfer the dish into your preheated oven.
Bake, uncovered for about 40 minutes, or just until a thermometer inserted in the center of each chicken breast reads 165°F.
Serve your saucey BBQ chicken warm.