Heat broiler to high. Halve the ciabatta or French bread lengthwise. Brush the insides with olive oil and toast for 2-3 minutes until golden brown to your liking.
In the bowl of a food processor, combine the arugula, cilantro, basil, dill, walnuts, feta, garlic, lemon juice, cumin, and a pinch of salt and pepper. With the processor running, slowly stream in the olive oil until emulsified. Taste and adjust seasonings as desired. This will make more than you need for the recipe.
Spread the pesto on the bottom half of the toasted bread, then the sundried tomatoes. Arrange the tomato slices and then the mozzarella. Finish with the arugula and, if desired, a drizzle of the sundried tomato oil. Set the top half of the bread and slice into 4-8 sandwiches.
Notes
*To store: The prepared sandwich will keep up to 3 days in the fridge if you use a sturdy loaf of bread.*Pesto: A few swaps you could try in the pesto: pine nuts for the walnuts (or any kind of nut, really), and parmesan for the feta. I just usually have feta around so it's what I use more often than not.