Lay each half of the focaccia bread on a cutting board, cut side up.
Combine mayonnaise and sundried tomatoes in a small food processor and pulse until combined. Spread mixture on one half of the focaccia, and the pesto on the other half.
Layer on the remaining ingredients.
Sandwich the two pieces of focaccia together and slice sandwich into quarters. Wrap up if you're taking on a picnic or enjoy right away. Best enjoyed within 1 day of making.
Notes
I used Trader Joe's Roasted Tomato and Parmesan Focaccia, but any local bakery should carry focaccia as well!