Prepare, bake and cool cakes in 2 or 3 loaf pans as directed on package; remove from pans. Line each of these pans with plastic wrap, allowing wrap to extend over edges. Place strawberries and sugar in food processor, cover and process, using 3 quick on-and-off motions, until coarsely chopped. Cut each loaf cake horizontally into 4 slices, using serrated or electric knife. Place 1 slice in bottom of each pan; spread 3 tablespoons of strawberry mixture over each. Top with another cake slice. Repeat with remaining strawberry mixture and cake slices. Cover with plastic wrap and refrigerate at least 2 hours until chilled.
To remove loaves easily from pans, place serving plate upside down on top of pan; turn pan upside down onto plate.