Slice each baguette into 3 even pieces. Slice each piece in half lengthwise to make top and bottom halves for 6 sandwiches.
Heat a pan over medium-high heat with a drizzle of olive oil. Place the onion rounds into the pan and then sprinkle with salt and pepper. Cook the onion until just tender and set aside, about 3 minutes per side. Cool completely and slice the rounds in half.
Roast the peppers by placing them directly on a gas burner and charring their skins evenly on all sides. Place them in a closed paper bag, or Ziplock bag until cool to loosen their skins. Peel all the peppers. Remove and discard the stems, piths and seeds.
Spread some cream cheese or goat cheese on both the top and bottom halves of the baguettes. Spread some pesto on top of the bottom halves only.
Top with the tomatoes and sprinkle lightly with salt and pepper. Arrange the cooked onion slices, roasted peppers and basil leaves over the tomatoes. Place the top pieces of baguette on top of the vegetables. You will end up with 6 3-inch individual sandwiches. Serve at room temperature.