How to Make It
Rinse and sort beans according to package directions. Heat 1 1/2 teaspoons canola oil in a large skillet over medium-high. Add 1 3/4 cups chopped onion, 1 cup chopped bell pepper, and, if desired, bacon; cook, stirring occasionally, until onions are tender, about 8 minutes. Add 3 teaspoons chopped garlic, and cook, stirring often, until fragrant, about 30 seconds.
Transfer onion mixture to a 6-quart slow cooker; add beans, jalapeño, chicken (or vegetable) broth, 1 1/2 teaspoon kosher salt, brown sugar, cumin, pepper, and oregano. Cover and cook on LOW until beans are tender, about 6 hours.
Heat 1 tablespoon canola oil in a large skillet over medium-high and cook sausage until browned, about 4 minutes. Using a slotted spoon, transfer sausage to a plate. Add 1 tablepsoon canola oil, shrimp, and Cajun seasoning to skillet. Cook until shrimp are opaque, 1 to 2 minutes per side. Remove shrimp to plate with sausage.
Cook pasta in salted water according to package directions; drain. Meanwhile, add 1 tablespoon canola oil; 2 teaspoon chopped garlic, 3/4 teaspoon kosher salt; and 1 cup chopped yellow onion and 1 cup chopped red bell pepper to skillet, and cook until tender, about 6 minutes. Remove from heat.
Add sausage, shrimp, 1 1/2 cups drained and rinsed black beans, hot cooked pasta, unsalted butter, and fresh lemon juice. Toss until butter is melted and pasta is evenly coated, about 3 minutes. Garnish with sliced scallions.