Creamy Chicken Penne

• 1 brown onion, finely chopped
• 2 garlic cloves, crushed
• 200 g white cup mushrooms, sliced
• 500 g chicken breast, diced
• 2 medium zucchini, grated
• 2 tbsp tomato paste
• 1 cup milk
• 200 g baby spinach
• 300 g wholemeal penne pasta