One Pot Tuna Pasta

• 500 g penne pasta
• 1 large brown onion, chopped
• 425 g tuna chunks in oil
• 800 g diced tomato, tinned
• 250 g cherry tomatoes, sliced in half
• 100 g feta
• 500 ml vegetable stock, salt reduced
• 500 ml water
• 0.5 cup bunch fresh basil, chopped