Step 1 Finely chop about a third of the cilantro to yield 2 tablespoons, setting aside the rest. In a small bowl, mix the chopped cilantro with the sour cream and set aside.
Step 2 In a medium saute pan over medium heat, toast the pumpkin seeds until they pop and turn slightly golden, 8 to 10 minutes; do not let them brown. Set aside briefly to allow to cool.
Step 3In a food processor or blender, place the pumpkin seeds, olive oil, garlic, salt, chiles, remaining cilantro and one-half cup of water. Blend to a smooth paste.
Step 4Return the mixture to the saute pan, add one-half cup of water and cook over low heat for about 20 minutes to develop the flavors. Stir frequently to make sure the sauce doesn't burn and add more water if the sauce thickens too much or too quickly. Meanwhile, shred the jicama using a box grater. Refrigerate until needed.
Step 5Increase the heat to medium-high and add the shrimp. Cover and cook until the shrimp are pink, about 5 minutes, stirring and turning the shrimp occasionally for even cooking.
Step 6Heat a skillet or griddle over medium heat and warm the tortillas. Arrange two tortillas per plate, slightly overlapping. Divide the shrimp among the tortillas, add shredded jicama and a spoonful of cilantro sour cream. Serve immediately, with lime wedges.