Wash and dry all produce. Halve, peel, and dice onion. Halve bell peppers through stem ends, then remove and discard core and seeds. Remove sausage from casings; discard casings.

In a large bowl, mix together sausage, onion, rice, 1/3 cup tomatoes, 1 TBSP Southwest spice, 1 TBSP olive oil, and a large pinch of salt and pepper (we’ll use the rest of the tomatoes and spice later).

In a medium bowl, stir together 1/2 cup water, 1 TBSP olive oil, and remaining tomatoes and Southwest spice. Season with salt and pepper. Pour half the mixture into your slow cooker.

Stuff bell pepper halves with filling, then nestle inside slow cooker cut-side up (it’s OK if they overlap). Cut 2 TBSP butter into 8 pieces and place one piece on top of each bell pepper half. Pour over remaining sauce. Cover slow cooker and cook stuffed bell peppers on high heat for 6 hours or low heat for 8 hours.

About 15 minutes before bell peppers are done cooking, trim, then thinly slice scallions, keeping greens and whites separate. About 10 minutes before cooking is done, scatter scallion whites and cheese over bell peppers in slow cooker. Cover and allow cheese to melt while the bell peppers finish cooking.

Divide bell pepper halves between plates. Spoon over any remaining sauce from slow cooker. Garnish with scallion greens and serve.