For the onion marmalade: Heat the oil in a heavy medium saucepan over medium heat. Add the onions and cook, stirring frequently, until the onions begin to soften but not brown, about 8 minutes. Add 1/2 cup water, the sugar and chile flakes. Cook the onions until almost all the liquid is absorbed, stirring often, about 12 minutes. Add the apple cider vinegar and simmer until the marmalade is thick, stirring often, 8 to 10 minutes. Sprinkle with salt and pepper and cool.
For the grilled sausages: Prepare a grill to medium-high heat. Brush the sausages with oil. Grill the sausages, turning them constantly, until golden and cooked through, or when an instant-read thermometer inserted in a sausage reads about 165 degrees F, about 14 minutes. Spread each baguette with the mustard. Place the grilled sausages on top of each baguette and top with the onion marmalade and Tomato Chutney.
Boil a pot of water. Prepare a bowl of ice water. Cut the stem of the tomatoes using a paring knife. Slice a shallow X in the bottom end of the tomatoes. Plunge the tomatoes into the boiling water for a few seconds, using a slotted spoon. Transfer the tomatoes to the ice water. Remove the tomatoes and peel away the skin. Chop the tomatoes roughly.
Pour the oil into a medium saucepan and heat over medium-high heat. Add the garlic and cumin and cook until fragrant, about 1 minute. Add the tomatoes, red wine vinegar and sugar and cook, stirring half way through the cooking time, until slightly thickened and the tomatoes have broken down, about 20 minutes. Add the herbs de Provence and sprinkle with salt and pepper. Cook the chutney, about 5 minutes. Let the chutney cool slightly before serving. Yield: 4 servings.