Cook penne according to package directions. Drain; reserving 1/4 cup (60 mL) pasta water.
In large skillet, heat 1/2 of the olive oil over medium heat; cook sausages for 3 minutes per side or until browned. Transfer sausages to cutting board; slice into 1/4 inch (5 mm) slices diagonally and set aside. Drain excess fat from skillet; in same skillet, heat remaining oil. Cook onion and garlic for 8 to 10 minutes or until tender and caramelized.
Add tomato sauce and roasted red peppers to skillet; bring to simmer. Return sausages to skillet. Add penne, reserved pasta water and spinach; toss to combine. Cook just until heated through and spinach is wilted.