In a large nonstick pan, heat 1 1/2 Tbsp. oil and garlic over medium heat for 2 minutes. Add onion; cook until it's translucent, about 4 minutes. Add tomatoes, juice and crushed red pepper, and simmer for 2 minutes. Add beans and salt, stir, cover and simmer for 20 minutes.
Heat a grill pan over medium-high heat and coat with cooking spray. Add sausages and cook on all sides until nicely grilled, about 10 minutes. Remove from pan and slice in half lengthwise. Return sausages to pan, cut side down and cook through, 5 minutes.
Just before serving, add arugula to beans, stir to combine, cover and cook for 3 minutes, or until arugula wilts. Add sage and remaining 1 Tbsp. oil. Serve with sausage.