Italian sausage, olive and ricotta pasta bake

Ingredients

• 1 tablespoon olive oil
• 500 grams pork and fennel sausages
• 2 red capsicum, seeded, sliced
• 1 red onion, thinly sliced
• 1/2 cup pitted kalamata olives
• 2 teaspoons fennel seeds
• 2 400g cans diced tomatoes
• 2 tablespoons red-wine vinegar
• 2 teaspoons caster sugar
• 500 grams penne pasta, cooked al dente
• 1 cup roughly chopped parsley
• 250 grams ricotta cheese
• 3/4 cup gruyere cheese, grated
• baby rocket leaves, to serve