Melt 1 Tbsp. butter in a small saucepan. Add 2 Tbsp. green onion and 1 tsp. garlic and cook over low heat until softened, about 3 minutes. Add beer and Worcestershire sauce and increase heat to medium-high. Boil to reduce sauce to 1 cup, 15 to 20 minutes. Remove from heat.
In a small bowl, combine cumin, herbes de Provence, salt, cayenne pepper, paprika, and ground black pepper. Set aside.
In a large sauté pan, heat oil until shimmering. Add remaining 4 Tbsp. green onion, remaining 2 tsp. garlic, and green and red bell pepper. Sprinkle with spice mixture and sauté until vegetables have softened, about 5 minutes. Add shrimp and sear on one side, about 1 minute. Flip shrimp and add reserved sauce, remaining 2 Tbsp. butter, and cream and bring to a simmer. When shrimp are pink on both sides, about 2 minutes, add spinach a handful at a time, stirring to coat with sauce. When spinach has wilted, remove pan from heat, stir in lemon juice, and serve immediately over Cheddar grits.