Preheat the oven to 400°F and place the rack in the middle.
Place the chicken thighs at the bottom of a large baking dish and season with salt to taste.
Chop the onion, slice the lemon into wedges, and mince the garlic.
Spread the onions, lemon, garlic, and olives around the chicken. Add 1 cup of coconut milk and season with tarragon. Transfer to the oven and bake until the chicken is cooked through, about 1 hour.
While the chicken is in the oven, peel and dice the sweet potato. Add to a pot along with the broccoli florets and cover with water. Cover and bring to a boil over high heat, then reduce to medium and cook until fork tender, about 15 minutes.
When the vegetables are done, drain the water and transfer to a food processor equipped with an S-blade. Add the remaining 1/2 cup of coconut milk and process until smooth and creamy, about 30 seconds. You may have to do this in 2 batches. Season to taste with salt.
To assemble: divide the ingredients evenly between 4 containers if you are meal prepping. Store in the refrigerator up to 7 days or freeze.