HEAT oven to 400ºF.
TOSS squash with oil. Spread onto baking sheet. Bake 15 min. or until tender. Meanwhile, flatten bread slices with rolling pin. Press 1 piece onto bottom and up side of each of 12 muffin pan cups sprayed with cooking spray.
COMBINE squash and tomatoes; spoon into bread cups. Beat remaining ingredients with whisk until well blended; spoon over squash mixture.
BAKE 15 to 18 min. or until centers of filling are set and tops are golden brown.