In a large skillet heat 1 tablespoon of the oil; add half the spinach and cook over moderately high heat, tossing with tongs, until slightly wilted, add the remaining spinach and toss and cook until wilted. Season with salt and transfer to a colander to drain.
In a small saucepan, combine the coconut milk, curry paste, sugar, lime zest and juice, and fish sauce - whisk to combine. Heat over low heat until simmering, cook, stirring occasionally, for about 10 minutes. Taste and adjust seasonings (and heat). Keep warm.
Wipe out the skillet used to cook the spinach. Over a fairly high heat, heat the remaining 2 tablespoons of oil. Lightly salt and pepper the scallop on both sides, place the scallops in the pan, in batches if necessary to not crowd the pan, you want sizzle, not steam, cook about 2 minutes per side. Set-aside cooked scallops while you finish remaining ones.
To AssembleI: n a large wide bowl, place the rice noodles, split the spinach evenly over each dish, then the carrot and onions, top with cooked scallops, then pour the curry sauce evenly over each bowl. Top with chopped nuts, and optional cilantro and/or Thai basil. Serve immediately.