In a blender, combine the garlic, ginger, peanut butter, cilantro, basil, mint, jalapeño, and sugar and pulse to form a paste. Place a strainer over the blender and squeeze the juice from the lemon, lime, and 1 of the oranges into the blender. With the motor running on low, slowly add the canola and sesame oils. Season with 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper; set aside.
Meanwhile, peel the remaining orange. Divide it into segments and cut each one crosswise; set aside.
Heat the grill to medium. Divide the shrimp among 4 skewers. Season with the remaining salt and pepper. Grill, turning once, until the shrimp are pink and cooked through, 3 to 4 minutes total.
Divide the spinach and orange segments among individual plates. Place one skewer on each salad and serve the dressing on the side.
Tip: You can make the dressing ahead of time and refrigerate it for up to 1 week.