Preheat oven to 375º. Butter a sheet pan.
Break up all bread by hand in a large pot. Add evaporated milk and mix well. Separate yolks from whites in two large bowls. Add sweetened condensed milk and vanilla to yolks and mix well until eggs are smooth and pale yellow.
Add egg mixture to bread. Place over low heat and stir. When bread starts to brown on the bottom, it’s done. Remove from heat.
Meanwhile, place guava paste in a frying pan. Add a little water to loosen mixture. You can cut it up a bit. Cook until it softens. Add fresh or canned guava pieces and heat together until guava pieces get soft.
Pour bread mixture into pan, making sure it’s even. Pour guava mixture evenly on top of bread. Bake for 15 minutes, or until set firmly.
While pan is in oven, make meringue: Beat egg whites to soft peaks. Add sugar and beat until soft peaks form. Top baked bread mixture with meringue and return to oven for 10-12 minutes, or until meringue browns. Remove from oven and let cool for 15 minutes. Cut in squares.