Whisk together the maple syrup and mustard in a small saucepan over medium heat and bring to a boil. Simmer until slightly thickened, about 5 minutes. Remove from heat and set aside.
Place the salmon in a foil-lined 9-by-13-inch baking dish. Season with the salt and pepper. Slice the peel from the pineapple half and cut it lengthwise into quarters, then cut each quarter into 1/2-inch-thick triangles. Scatter the pineapple and jalapeño around the salmon. Brush the salmon with the syrup mixture. Broil for 5 to 7 minutes, or until the salmon flakes easily when pricked with a fork and the inside is the same color throughout. Serve the salmon and pineapple with the rice and drizzle with the remaining glaze, if desired.
Tip: Slice the other half of the pineapple left over from this recipe, brush it with maple syrup, and broil until it bubbles. Serve with ice cream.