Heat your oven to 180F/200C. Stab your squash all over with a fork and then place it in the oven for 1 hour to roast.
Meanwhile, make your pesto by combining the walnuts, Parmesan, garlic and basil in a food processor, blend to form a think chunky paste. Pour in the olive oil whilst blending until you have the consistency you would like, be it runny or thick, up to you! Then squeeze in the lemon juice and season. Use the cream to loosen if you like.
Fry your chicken in a pan with a little oil until cooked through. Stir through the pesto at the last minute just to warm.
Remove from oven, cut in half length ways and scoop out the seeds. Then, using a fork, fork the flesh away from the skin to make strands of spaghetti squash. Divide your spaghetti squash between two bowls and spoon over the walnut pesto chicken.