Tear the chard leaves into large pieces; cut the stems into 1-inch pieces. Heat the olive oil in a large skillet over medium heat. Once hot, add the garlic and cook until fragrant. Toss in the greens and stems by big handfuls. Stir and toss around with tongs, and cook until wilted. Season with some salt and pepper.
Add the cannellini beans, sundried tomatoes and red pepper flakes and toss. Once ingredients are incorporated, remove from heat, top with the red onion and serve.