Beef and vegetable lasagne

Ingredients (serves 4): 500g lean beef mince 1 red onion, finely chopped 2 garlic cloves, crushed 1 medium carrot, grated 3 celery stalks, finely chopped 1 medium green bell pepper (capsicum), finely chopped 200g small button mushrooms, thinly sliced 2 tablespoons tomato paste 2 x 400g cans diced tomatoes with oregano and basil Olive oil spray…