To make the sofrito, pulse together the onion and pepper in the bowl of a food processor to break them down. Pulse in the jalapeno and garlic and then add the cilantro and tomatoes and puree into a course mixture. Set aside.
Heat a drizzle of olive oil in a paella pan over medium heat. Sprinkle the chicken with salt and pepper and then add them to the pan skin-side down. Cook without moving too much until golden brown and crisp, 5 to 6 minutes. Flip and brown on the other side for 1 to 2 minutes. Remove to a plate and set aside.
Add the chorizo to the pan and cook until it has rendered its fat. Add in the sofrito with a good pinch of salt and cook until fragrant and the sofrito begins to toast and dry out, 3 to 5 minutes. Stir in the tomato paste and toast until rusty in color, about 1 minute.
Add the rice and toast briefly. Deglaze the pan with the white wine. Add the paprika and cumin and then slowly add the stock, stirring as you add. Nestle the chicken back into the pan and bring to a simmer. Arrange the clams around the chicken and cook for 2 minutes. Add the mussels and shrimp and cover the pan. Cook until the clams and mussels have opened and the rice is tender and crisp on the bottom, 15 to 20 minutes.
Discard any clams or mussels that didn't open. Garnish with freshly ground pepper and some torn cilantro. Serve.