Combine the flour, 1 teaspoon of salt, and 1/4 teaspoon of black pepper in a gallon zip-top bag. Pat the trout dry and toss to coat in the bag with the seasoned flour.
Heat the olive oil in a 12-inch saute pan set over medium-high heat until it shimmers. Carefully add the trout to the pan. Cook on each side for 1 minute.
Using tongs or a fish spatula, transfer the trout to a 13 by 9-inch glass baking dish. Reduce the heat to medium, add the onion, and cook until translucent, approximately 5 minutes. Add the garlic and cook for an additional minute. Add the remaining 1/2 teaspoon salt, 1/4 teaspoon black pepper, thyme, coriander, paprika, white wine, vinegar, and lemon zest. Decrease the heat to low and simmer, uncovered, for 10 minutes.
Remove from the heat and pour the marinade over the trout. Refrigerate, uncovered, for at least 1 hour before serving. Serve cool or at room temperature with the sauce and onions. Refrigerate, covered, for up to 12 hours.