Preparation

• Season the shrimp with 1/4 tsp. salt, a few grinds of pepper, and 1 tsp. chili powder. Set a heavy 10-inch skillet over medium-high heat for 1 minute. Add the oil and shrimp and sauté, stirring occasionally, until the shrimp are opaque and firm to the touch, about 2 minutes. Transfer to a cutting board.
• Pit the avocados and scoop the flesh into a small bowl. Add 1 Tbs. lime juice, the chopped cilantro, and a pinch of chili powder. Mash with a fork until relatively smooth and season with a heaping 1/2 tsp. salt and a few grinds of pepper. Slice the shrimp in half lengthwise.
• To assemble, spread the mashed avocado over the toasts and slice each toast into four even rectangles.  Top each with two halved peices of shrimp and a cilantro leaf, sprinkle with lime juice and salt, and serve.  (The rectangles can be cut into squares for even smaller bites.)