Feta & Tomato Tart advice

I made this Feta and Tomato Tart recently and the flavors were AWESOME, explosive. My problem was it was a bit runny so was wondering what I could do to tighten up the juices in the tart? I know in a pie you'd put a little tapioca in it but not sure that would be the right thing for this dish. Could I sprinkle corn starch in it? Thanks! Lana

Feta and Tomato Tart

9" Pastry Shell, uncooked
3 Tomatoes, peeled & sliced (I used locally grown hydroponic tomatoes that have good flavor)
3/4 C Mayonnaise (I used fat-free)
6oz Feta plain crumbled ( I used President Herbed Feta w/Tomato & Basil fat-free)
1 C Mushrooms sliced (I forgot to put in the mushrooms lol)
1T Onion (I used more but it was a sweet, mild onion)
1T Green Bell Pepper (I used Red Bell and lots more than 1T because I love the flavor)
1/4 C Basil, chopped (I probably used more of this as well as we love fresh Basil)
Salt and Pepper to taste (I used fresh ground pepper from mixed pepper berries)

Directions;
Arrange half of tomato slices in pastry shell.

Combine mayonnaise, feta, mushrooms, onion, green pepper and basil stirring well. Spread half of mixture over tomato slices. Repeat layers with remaining tomatoes and mayonnaise mixture. Bake at 350 degrees for 30-35 minutes. Set aside and allow to cool for 10-15 minutes before serving.