Cook spaghetti according to instructions on package. Reserve one cup of pasta water to finish pasta with once it is cooked.
In a large pot or a deep saucepan, add the kale pesto and roasted tomatoes along with a cup of pasta cooking liquid. Warm this mixture over low heat to preserve the colour and flavour of the kale pesto.
Add your preferred amount of cooked pasta and toss or stir to coat evenly in the pesto sauce. Add pasta water as necessary to achieve the consistency of sauce to your liking.
Garnish with grated Grana Padano and chili flakes if desired.