In a large skillet over medium heat, toast coriander and cumin, stirring frequently, until fragrant and slightly darkened, 3 to 4 minutes. Let cool slightly. Transfer to a spice mill or mortar and pestle and grind into a powder. Wipe out skillet.
Transfer ground spices to a medium bowl. Add lemon zest, chili powder, 1 Tbsp. oil, and 1 tsp. salt, then add shrimp. Toss to coat and let marinate at room temperature for 10 minutes.
Meanwhile, finely chop cilantro, parsley, and oregano and transfer to a medium bowl. Add garlic, vinegar, red pepper flakes, 3 Tbsp. oil, and 3/4 tsp. salt and stir to combine.
In same skillet over medium heat, swirl remaining 1 Tbsp. oil to coat pan. Add shallot and remaining pinch of salt and cook, stirring occasionally, until shallots start to brown around the edges, 3 to 4 minutes. Add shrimp and any remaining marinade to pan in a single layer. Cook, undisturbed, 2 minutes, then turn shrimp. Add stock and bring to a simmer. Cook, stirring occasionally, until shrimp is pink and cooked through, 1 to 2 minutes more.
Top with chimichurri. Serve with lemon wedges and bread.