Sear the Goose: Heat olive oil in a pan over medium-high heat. Sear the goose breasts for 2 minutes per side until browned. Transfer to the crockpot.
Prepare the Flavor Base: In the same pan, sauté onions and garlic until fragrant (about 3 minutes). Pour in the red wine and let it simmer for 2 minutes to reduce.
Assemble in the Crockpot: Add the sautéed onions and garlic to the slow cooker. Pour in the broth, Worcestershire sauce, balsamic vinegar, smoked paprika, thyme, salt, pepper, and bay leaf.
Slow Cook: Cover and cook on Low for 6 hours or High for 3.5 hours until tender.
Finish the Sauce: Remove the goose and let it rest. Strain the cooking liquid, then reduce it in a pan with butter for a thicker, richer sauce.
Serve: Slice the goose breast and drizzle with the sauce. Serve with mashed potatoes or roasted vegetables.