Preheat oven to 400 degrees. Grease a 9X13 baking dish (2 1/2- 3 quart dish) with cooking spray.
Add brown sugar, vinegar, and salsa to baking dish and stir until sugar dissolves.
Heat the olive oil in a small frying pan on stove and cook the onions for 3-4 minutes until they just start to become translucent. Do not brown them.
Add all remaining ingredients, including sautéed onions, but NOT the beer and the bacon, into the baking dish and mix to combine. Pour the beer over the mixture and stir until combined. If desired, lay the beacon strips on top.
Bake 1 to 1 1/2 hours, until reduced and thickened, but not dry. Discard bacon strips and serve.