Bring a large pot of salted water to a boil. Add the shrimp and boil until they turn pink, 1-2 minutes. Drain and cool.

​Stand the grapefruit on end and carefully slice straight down each side, removing peel, pith, and membrane. Turn it on its side and cut off top and bottom. Remove sections from membrane and break into bite-sized pieces. Drain any excess juice.

​In a large serving bowl, combine the chile paste (optional), lime juice, fish sauce, sugar, and jalapeno. Stir until the sugar dissolves. Add the shrimp, grapefruit, mint, fried shallots and garlic, and peanuts and toss to mix. Garnish with the cilantro and serve at once.