Combine basil, garlic and walnuts in a food processor and chop well. Slowly drizzle in olive oil, keeping processor going. Once oil is combined, turn off processor and add cheeses, salt and pepper. Stir to combine. Keeps well in refrigerator for up to a week.
To make sandwiches: Cut baguette into sandwich-size pieces. Cut each piece down the center, leaving one side intact. Slather bread with pesto. Slice four tomatoes thinly and distribute between sandwiches.