In a blender, puree the 1/3 cup of basil leaves with the olive oil until smooth. Season the oil with salt and black pepper.
Light a grill or preheat a grill pan. In a small bowl, mix the sweet smoked paprika with the pure ancho chile powder, light brown sugar, cumin, coriander, cayenne pepper, 1/2 teaspoon of salt and 1/4 teaspoon of black pepper. Brush the shrimp with the canola oil and season all over with the spice mixture. Grill the shrimp over moderately high heat, turning once, until they are lightly charred and cooked through, about 4 minutes total.
Arrange the tomato and onion slices on a platter and drizzle with the basil oil. Top with the shrimp, garnish with the remaining basil leaves and serve.