For the salsa negro, remove the stems and seeds from the chilies and chop into small, ¼-inch pieces.
Add sesame seeds, cumin seeds, garlic, and oil to a medium saucepan over medium-high heat. Cook for 4-5 minutes or until the garlic is lightly golden. Remove from the heat and cool for 10 minutes. Add chilies, vinegar, soy sauce, and oregano. Allow to cool for 30 minutes.
Once cooled, add the mixture to a food processor and pulse just until it's combined, but still coarse.
For assembly, add the shrimp to a bowl and cover with lime juice, reserving 2 Tbsp. Let sit for 20 minutes and then strain.
Toss shrimp with ¼ cup of the salsa negro and the reserved 2 Tbsp of lime juice. Season with salt to taste.