Preheat the oven to 375°F (190°C, or gas mark 5). Line a sheet pan with parchment paper. Soak the skewers (if using), in a shallow dish of water while preparing the sauce.

Combine the chili garlic sauce, lemon juice, lime juice, sesame oil, soy sauce, peanut butter, maple syrup, and smoked paprika in a bowl.

Cut the tempeh in three strips lengthwise and then quarter each strip into 4 triangles for 12 thick triangles in total. The ends will be square but cut the remaining parts into triangles. Toss the pieces in the bowl until completely coated. Add 3 pieces to each skewer (if using). Transfer the tempeh to the prepared sheet pan.

Use a spoon to drizzle the marinade on each piece. Bake for 10 minutes. Then flip tempeh and use a spoon to drizzle more marinade on the pieces. There should still be about ¼ cup (60 ml) marinade left. Hold on to it. Bake for 10 minutes, until dry. If desired, turn the oven up to broil and broil for 1 to 2 minutes to lightly char the edges.

Transfer the tempeh to a serving dish. Drizzle with remaining marinade, and sprinkle with crushed peanuts and scallions (if using).