Blanch the green beans in salted water and keep aside.
Cook the pasta in boiling water according to packet directions. Drain and keep aside, reserving 1 cup water.
Heat oil in a large pan and add onion and garlic, cook for 1 min or until softened. Add tomatoes, thyme and chilli flakes and cook for 3 mins, or till the tomatoes have softened and turned mushy. Season to taste with freshly ground black pepper and salt.
Add the beans and canned tuna (with the chilli) to the tomato mixture. Lightly break up the tuna if necessary with the ladle and mix well to combine.
Then add pasta and the reserved pasta water; toss well to combine. Season with salt and pepper.