Makes: 8 appetizer servings. Prep: 5 minutes. Cook: about 4 minutes per batch.
Crush the cumin, coriander and mustard seeds in a spice grinder or in a mortar with a pestle. Toss the shrimp with crushed spices, cayenne, salt and pepper in a large bowl. (Can be prepared ahead and chilled until ready to cook.)
Heat the olive oil in a large skillet over medium-high heat. Add just enough shrimp for a single layer; cook until shrimp is pink and spices are toasted and smoky, 1 to 2 minutes on each side.
Place the cooked shrimp in a large bowl. Cook remaining shrimp. Squeeze lemon juice over shrimp, toss with parsley and transfer to a large serving platter.