In a medium saucepan, bring 3 1/2 cups water to a boil. Add 1/2 tsp. salt. Pour in polenta in a thin stream, whisking constantly, and whisk until mixture comes to a steady simmer. Reduce heat to maintain a gentle simmer, cover, and stir every 5 minutes until done, about 25 minutes total.
Meanwhile, in a large frying pan over medium-high heat, cook bacon until fat renders and edges start to brown and crisp. While bacon cooks, trim stems and ends of green onions, leaving onions as intact as possible. Drain bacon on paper towels, chop, and set aside.
Remove all but 1 tbsp. bacon fat from the pan. Add whole green onions and cook until soft and starting to brown, about 3 minutes; turn and brown opposite sides, about 3 minutes more. While green onions cook, halve tomatoes along the equator and sprinkle cut sides with salt and pepper. Chop garlic. Set both aside.
Transfer green onions to a baking sheet or platter and cover to keep warm. Put tomato halves cut side down in pan with bacon fat and cook until starting to brown, about 3 minutes. Turn and cook until heated through and a bit soft, about 3 minutes more. Transfer to baking sheet with green onions to keep warm.
Add garlic to pan and cook, stirring, until fragrant, about 1 minute. Add shrimp and cook, stirring constantly, until starting to turn pink, 1 to 2 minutes. Pour in wine and continue cooking, stirring and scraping up any browned bits from the pan, until shrimp is cooked through, about 2 minutes. Remove from heat.
Stir butter, cheese, and bacon into polenta. Divide polenta among 4 to 6 plates and top with shrimp and remaining liquid in the pan, dividing evenly. Set a tomato half and several green onions beside polenta. Serve immediately.
Note: Nutritional analysis is per serving.