Place asparagus spears into a large skillet, and pour in enough water to cover the bottom of the skillet about 1/2 inch deep.
Place skillet over medium heat, bring to a boil, and reduce heat to medium-low. Simmer until the water has evaporated, about 5 minutes.
Stir unsalted butter and pecans into the skillet with asparagus, and let simmer until asparagus are beginning to brown and pecans are fragrant, about 2 more minutes.
Remove from heat.
Season salmon fillets with salt and black pepper and set aside for about 5 minutes; pat off any excess moisture with paper towels.
Heat olive oil in a skillet over medium-high heat, and pan-fry the salmon fillets in the hot oil until browned and the flesh flakes easily and is nearly opaque in the center, 4 to 5 minutes per side. Squeeze half a lemon over the salmon fillets as they cook.
Fill a large pot with lightly salted water and bring to a boil; stir in the angel hair pasta, and return to a boil. Cook the pasta uncovered, stirring occasionally, until cooked through but still slightly firm, 4 to 5 minutes.
Drain well and return to saucepan.
Stir 2 tablespoons butter, parsley, and basil into the cooked pasta until coated; sprinkle with salt and black pepper to taste.
To make sauce, melt 2 more tablespoons of butter in a small saucepan over low heat until melted; stir in Dijon mustard, and squeeze remaining lemon half into the sauce. Allow to simmer for about 3 minutes to blend flavors.
To serve, divide angel hair pasta between two plates, top each serving of pasta with half the asparagus and pecans, and arrange a fillet over the asparagus. Spoon Dijon dressing over fillets to serve.
