Heat the olive oil in a large heavy-bottom pot, and add the diced leeks. Saute for 2 minutes, then add the rice, chicken/fish stock, and 3 cups of water.
Add the hot pepper flakes, lemon zest, lemon juice, and turmeric. Add 1/2 tablespoon salt and stir well.
Bring to a boil, then cover and simmer on low heat for about 15 minutes, or until the rice is almost done. After 15 minutes of cooking there should be just a bit of liquid remaining, and it would get cooked down in the next three steps. If the liquid gets absorbed too early, add a bit more water, a half a cup at a time.
Carefully taste the paella broth and see if you need more salt (don't burn your mouth!). If you need more salt, gradually add more (up to a tablespoon total) until it is to your liking.
After the rice has been cooking for 15 minutes (when it is just about done), add the vegetables - bell peppers, asparagus, and peas. Stir them into the paella and cook for 3 minutes. At this point, look at how much liquid you have and turn up the heat if it looks like too much liquid.
Stir in the seafood mix, making sure to cover all the seafood in the saucy paella completely. If your seafood is thawed, continue to cook for about 3 minutes, or until it is fully cooked. If your seafood is frozen, cook for about 5 minutes, or until everything is fully cooked. Remove from heat and garnish with fresh chopped parsley to serve.