Place the tomatoes in a grill pan and cook under a preheated hot grill for 10 minutes, turning once. Add the garlic and cook for a further 3–5 minutes until softened and charred. Leave to cool slightly, then transfer to a food processor or blender, add the chipotle paste and whizz to a coarse paste. Season and set aside.
Heat the oil in a large frying pan, add the pasta nests and cook for 1–2 minutes until starting to brown, then turn the pasta over and cook for a further 1 minute. Remove from the pan.
Add the shallot to the pan and cook for 3 minutes until softened, then add the tomato sauce and stock. Bring to the boil, then reduce the heat and simmer for 15 minutes.
Return the pasta to the pan and cook gently, stirring frequently, until the pasta is tender and most of the liquid has been absorbed.
Spoon the pasta on to serving plates and scatter over the crab meat. Serve with lime wedges.