Fill a pan with 500ml cold water and drop in the rosemary sprigs.
Finely chop the parsley stalks, saving the leaves for later. Peel and grate or crush 1 garlic clove. Halve and deseed the chilli. Finely chop it. Peel the onion and thinly slice. Pop everything in the pan with the water. Crumble in the stock cube and pour in 1 tbsp olive oil.
Lower in the chicken breasts. Add a little more water if the water doesn't cover them. Pop on a lid and bring the water up to the boil. As soon as the water is bubbling, lower the heat and simmer for 12 mins. Skim off any white froth from the surface.
While the chicken is cooking, finely shred the rainbow chard leaves and stalks. Zest and juice the lemon. Peel and grate the remaining garlic clove. Roughly chop the parsley leaves.
Lift the chicken out of the pan and place on a plate. Cut into the thickest part of the breast and check that there is no pink. If there is, pop it back in the broth for a few more mins. Cover with foil to keep the chicken warm.
Drop the tortelloni into the broth. Add the rainbow chard on top. Pop on a lid. Simmer for 4 mins.
While the tortelloni is cooking, mix the lemon juice, zest, garlic and parsley leaves with 1 tbsp olive oil and plenty of seasoning. This is your gremolata. Thinly slice the chicken breasts.
When the tortelloni is cooked, ladle the pasta, broth and rainbow chard into a couple of warm bowls. Top with a sliced chicken breast each. Drizzle over the gremolata to serve.