Chard-Wrapped Fish with Lemon and Olive

Finely zest and juice both lemons. Reserve the juice and half the zest. In a small bowl, combine the remaining zest with the olives, 1 tablespoon of the olive oil, 2 tablespoons of the chopped cilantro leaves, 1 teaspoon garlic, and the red pepper flakes until incorporated.
Bring a small pot of water to a boil over medium-high heat. Use a knife to separate the leaves from the chard stems so you have 2 leaves from each stem. Thinly slice the stems crosswise. Dip the chard leaves in the boiling water for 10 seconds to soften; drain, cool slightly, and pat dry. Cut the fish into 8 equal-sized pieces, season with salt and pepper, and spread 2 teaspoons of the olive mixture on each piece of fish.
Place 1 piece of fish on a piece of chard and roll it up; use the extra 2 leaves to patch any parts that need extra wrapping. Heat the remaining 3 tablespoons olive oil in a large skillet over medium heat. Add the onion and cook, stirring, until tender and lightly golden, 8 to 9 minutes. Add the chard stems with the remaining 3 teaspoons garlic and cook, stirring, until softened, 3 to 4 minutes. Add the flour and cook, stirring, until absorbed, 1 minute. Add the reserved lemon zest and juice with the stock, salt, and pepper and cook, stirring, until the liquid thickens and bubbles, 2 to 3 minutes. Stir in most of the remaining cilantro.
Nestle the fish in the skillet, scatter the tomatoes and whole olives over the fish, reduce the heat to medium-low, cover, and cook until the fish is opaque and the chard can be cut easily, 10 minutes. Serve over the grain of your choice with sauce spooned over the top; garnish with cilantro.