Roast the vegetables, do not boil them. The sweet potato and pepper go in the oven for a reason: it is where the sweetness and the edges come from, and a dal made with them simmered instead tastes flat however long you cook it.
The lime goes in at the end, off the boil. It is there to lift everything, and heat takes that straight back off again.
It thickens overnight. Red lentils keep drinking, so what is a soup this evening is close to a purée tomorrow. Loosen it with a splash of water or stock when you reheat rather than adding more coconut milk.
Spinach only needs to wilt. Stir it through the hot pan and take it off; it does not want cooking.