In a small bowl, whisk together the mustard, maple syrup and olive oil. Spoon the mixture over the salmon, then coat the top with the chopped pecans, pressing gently so they adhere. Bake for 12 to 14 minutes, or until the salmon is almost cooked through and the nuts are lightly browned. A good rule of thumb for fish is about 10 minutes of cooking time per inch of thickness. If the pecans begin to brown too quickly, loosely cover the salmon with foil. Serve warm.