Heat the olive oil in a skillet over medium heat. Add the onions and brown sugar and saute for 15 minutes, stirring occasionally, until the onions begin to caramelize.
Put the onions in the slow cooker and then add all the additional ingredients. Stir until everything is well combined.
Cook on low heat for 8 hours or high heat for 4 hours, stirring occasionally.
Check the seasonings, add more salt, pepper, or spices, and serve over top of pasta.