Grind walnuts, flour and 1/4 teaspoons each of salt and pepper in a food processor.
Coat nonskin side of trout with mixture and set aside.
In a large cast iron or nonstick skillet, saute garlic and shallot in 2 teaspoons of olive oil over medium heat for 3-4 minutes. Transfer to a blender and add broth, cilantro, lemon juice and remaining salt and pepper. Puree until smooth.
Heat remaining oil in the same skillet over medium heat. Cook trout fillets for 1 minute per side. Pour cilantro broth over fillets and cook until fork tender (3-4 minutes). Serve on plates with remaining cilantro broth spooned over fillets.