Preheat the oven to 425 degrees F (220 degrees C). Line a baking sheet with aluminum foil and grease with cooking spray.

Combine 2 tablespoons olive oil, rosemary, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a large bowl until well combined. Add potatoes and toss to coat. Place potatoes, skin-side down, in a single layer on the prepared baking sheet.

Roast in the preheated oven until potatoes are tender when pierced with a fork, 23 to 25 minutes. Remove from the oven; stir.

Mix together remaining 2 tablespoons olive oil, remaining 1/2 teaspoon salt, remaining 1/4 teaspoon pepper, onion flakes, paprika, parsley, and oregano in the same large bowl until well combined. Add sausage, green beans, bell pepper, and onion; toss until evenly coated. Add sausage mixture to potatoes on the baking sheet; spread out in a single layer.

Roast in the preheated oven until vegetables are tender and potatoes and sausage pieces are browned, 20 to 25 minutes, tossing halfway through the cook time.