Peel and finely chop the onion. Peel and grate or crush the garlic. Finely slice the mushrooms. Chop the chicken into bite-sized chunks.
Heat 1 tbsp oil in a deep frying pan or wok. Add the chicken. Season with a pinch of salt and pepper. Cook and stir over a medium-high heat for 5-6 mins till the chicken is golden brown. Lift out of the pan and pop onto a plate.
Add the onion to the frying pan. Turn the heat down to low. Cook for 5 mins till soft and glossy. Stir every so often.
Add the garlic and mushrooms to the frying pan. Cook for 5 mins till the mushrooms are lightly browned. Stir now and then.
Meanwhile, fill a pan with water. Add a pinch of salt. Cover and bring to the boil. Add the pasta. Put the lid back on and simmer for 8 mins till the pasta is tender but still has a little bite to it.
Pop the chicken back in the pan with the veg. Add 2 tbsp water and cook together for 2-3 mins to heat everything through.
Drain the pasta. Stir the crème fraîche into the chicken and veg. Gently warm for 1-2 mins. Add the pasta. Toss to mix. Pop onto two warm plates and serve topped with rocket.