Combine tomatoes, stock, wine, 1 1/2 teaspoons vinegar, paprika, and 1/4 teaspoon salt in a blender; process until smooth. Transfer mixture to a small saucepan over medium-high heat; bring to a boil. Simmer 10 minutes, stirring occasionally; remove from heat.
Heat a nonstick skillet over medium-high heat. Add 1 1/2 teaspoons oil. Sprinkle salmon with 1/4 teaspoon salt and 1/4 teaspoon pepper. Add salmon to pan. Cook 4 minutes on each side.
Combine remaining 1 1/2 tablespoons vinegar, remaining 1/4 teaspoon salt, remaining 1 1/2 tablespoons oil, remaining 1/4 teaspoon pepper, cashews, and onions in a bowl; toss to coat.
Divide stock mixture among 4 bowls. Place 1 salmon fillet in each bowl; top fillets with cashew mixture.