4 green onions, white and green parts separated, thinly sliced
1 garlic clove, minced
1 teaspoon dried oregano
Coarse salt and freshly ground pepper
Lemon wedges, for serving
Slice a very thin layer from the base of each bell pepper so they sit flat. Slice off tops just below stem. Discard stems; chop tops, and place in a medium bowl. Remove ribs and seeds from peppers.
Add beans, feta, couscous, scallion whites, garlic, and oregano to bowl. Season with salt and pepper and toss to combine. Stuff peppers with bean mixture; place upright in slow cooker. Cover; cook on high, 4 hours.
Sprinkle peppers with scallion greens; serve with lemon wedges.
To make in the oven: Preheat oven to 350 degrees. In step 2, use a 5-quart Dutch oven or ovenproof pot with a tight-fitting lid; add 1 cup water. Cover; bake until peppers are tender, about 1 hour. Proceed with step 3.