Divide Chive Piecrust dough into 5 equal portions. Place each portion between two sheets of plastic wrap; roll into a 6-inch circle. Remove top sheet of plastic wrap. Place each dough circle, plastic wrap side up, into a 4-inch round tart pan coated with cooking spray. Remove remaining plastic wrap. Press dough into bottom and up sides of pan; fold excess crust back in, and press. Pierce bottom and sides of dough lightly with a fork; freeze 10 minutes. Line bottoms of dough with foil; top with pie weights or dried beans. Bake at 400° for 25 minutes or until lightly browned. Cool on a wire rack 15 minutes; remove weights and foil. Brush crusts with mustard.
Reduce oven temperature to 375°.
Combine 1 cup boiling water and porcini mushrooms in a bowl; cover and let stand 20 minutes. Strain mixture through a sieve over a bowl, reserving mushrooms and 1/4 cup liquid. Finely chop mushrooms.
Heat oil in a large skillet over medium heat. Add shallots; cook 1 minute. Add cremini and shiitake mushrooms; cook 8 minutes, stirring occasionally. Add garlic; cook 1 minute, stirring occasionally. Stir in porcini mushrooms, wine, and thyme; cook 1 minute. Add reserved 1/4 cup soaking liquid, scraping pan to loosen browned bits. Reduce heat; cook 3 minutes. Stir in parsley, juice, pepper, and salt.
Divide mushroom mixture evenly among prepared crusts. Combine 2 tablespoons cheese and next 4 ingredients (through egg white), stirring with a whisk; divide mixture evenly among tarts. Sprinkle tops evenly with bell peppers and remaining cheese. Place tarts on a baking sheet. Bake at 375° for 35 minutes or until set. Cool on a wire rack 10 minutes. Sprinkle with chives.