Place the chopped onions in the base of the slow cooker.
Put half of the sweet potato and butternut squash in with the onion.
Place the chicken breasts on top of the vegetables.
Spread 1 teaspoon of pesto over each chicken breast, season with salt and pepper and sprinkle over the oregano.
Put the rest of the sweet potato and butternut squash, and the cherry tomatoes, around the chicken breasts.
Measure the boiling water (150 ml or ½ cup) in a jug and add the chicken stock melt. Stir to melt it and then carefully pour the stock under the chicken in the vegetables.
Cook on low for 5-6 hours.
Check the chicken is cooked through.
Using a large slotted spoon, lift the chicken breasts out of the slow cooker and place them in a serving dish. Put the cooked vegetables around the chicken and serve.
Notes
Serving suggestion: Delicious with crusty bread, pasta, rice or couscous.