In a small bowl, stir to combine the sour cream, lemon juice, and salt. Set aside.
Meanwhile, lightly season the salmon on both sides.
In a large skillet or saute pan, heat 2 tablespoons of the olive oil over medium-high heat.
When the oil is hot, add the onions and cook just until beginning to get translucent,
about 3 minutes. Spread the onions out so they cover the bottom of the pan. Place the
salmon fillets on top of the onions and lower the heat to medium-low. Top the salmon
with the lemon slices. Cover and cook until the salmon is just cooked through and the
onions are caramelized, about 8 to 10 minutes. Be careful not to burn the onions while
the salmon is cooking. If they begin to burn, add a little water to moisten them.
While the salmon is cooking, cook the egg noodles in a large pot of boiling, salted water.
Drain and toss with remaining olive oil, salt, and scallions.
Divide the warm noodles among 4 large plates. Place 1 salmon fillet and the sauteed
lemons and onions over each serving of pasta. Top with the sour cream sauce and drizzle
with the olive oil. Serve.