Heat the oven to 375 degrees. In a large bowl, thoroughly combine the guavas, apples, dried cherries or cranberries, guava nectar, flour and vanilla. Divide evenly among eight 4 to 5-inch individual ovenproof serving dishes.
Place the flour, cornmeal, brown sugar, cinnamon and salt in a large bowl. Mix until thoroughly blended. Add the butter. Use a fork or back of a spoon to work the butter into the dry ingredients. Dribble in the milk and sprinkle with pepitas. Mix to combine. The mixture should hold together, but still be a little crumbly. Top each of the individual dishes of filling with about 1/2 cup of the streusel topping.
Bake in the lower third of the oven until the streusel topping is crisped and golden, 25 to 30 minutes. Serve warm, or let cool completely and reheat before serving. Top with vanilla ice cream if desired.