Strain the cream mixture through a chinois, adjust the salt, and reserve warm for later use.
Pop the popcorn on the stovetop with the canola oil, or use a popcorn maker.
Fill a blender halfway with the cream mixture. Add the popcorn until the blender cup is full. Blend the mixture until smooth, adding popcorn until you reach the desired thickness. Strain the mixture through a chinois or fine mesh strainer. Repeat for the remaining cream and popcorn. Adjust the seasoning with salt and finely ground pepper. Reserve in a warm place until ready to use.
Heat the oil in a skillet until just smoking. Add the fish to the pan, floured-side down, and turn the heat to medium-high. Cook the fish three-quarters of the way through on that side, and then flip. Add the butter to pan and baste. Cook until just before the fish wants to flake apart when pushed.
Saute the mushrooms and potatoes in the same pan, adding more butter if necessary, until golden brown. Add the spinach and cook to wilt. Add 1/2 cup of the popcorn sauce and the parsley to the pan. Adjust the seasoning with salt, pepper and some lemon juice. Arrange the vegetables in 4 large bowls and spoon some more sauce over the vegetables. Top each bowl with the sauteed walleye, then garnish with the parsley and dust with the smoked paprika.