Grill or toast bread. Lightly rub with peeled garlic clove, if desired. Discard the garlic.

Heat 2 teaspoons oil in a large nonstick skillet over high heat until shimmering but not smoking. Add chicken; cook, stirring occasionally, until just cooked through and no longer pink in the middle, 4 to 5 minutes. Transfer the chicken and any juices to a plate; cover to keep warm.

Add the remaining 2 teaspoons oil to the pan. Add chopped garlic and cook, stirring constantly, until fragrant but not brown, about 30 seconds. Add broccoli rabe (or broccolini) and cook, stirring often, until bright green and just wilted, 2 to 4 minutes. Stir in tomatoes, vinegar, salt and pepper; cook, stirring occasionally, until the tomatoes are beginning to break down, 2 to 4 minutes. Return the chicken and juices to the pan, add feta cheese and stir to combine. Cook until heated through, 1 to 2 minutes. Serve warm over garlic toasts.

Ingredient Note: Pleasantly pungent and mildly bitter, broccoli rabe, or rapini, is a member of the cabbage family and commonly used in Mediterranean cooking. Broccolini (a cross between broccoli and Chinese kale) is sweet and tender - the florets and stalks are edible.