In a large pot, heat the oil over medium-high. Add the red bell pepper, stemmed, seeded, and thinly sliced, the jalapeno, stemmed and thinly sliced. Cook, stirring occasionally, until onion begins to soften, about 3 minutes.

Add the rabe (about 1 pound), trimmed, cut into 1 1/2-inch pieces; season with the salt and the pepper and cook, stirring occasionally, until vegetables are crisp-tender, about 4 minutes. Stir in the red-wine vinegar, and the sugar and cook 1 minute. Serve warm or at room temperature.