Place raisins in a food processor; pulse into a paste.
Transfer raisin paste to a large bowl. Add oats and almonds.
Place banana in the food processor; blend into a puree.
Combine 1/4 cup banana puree, peanut butter, vanilla extract, and salt in a saucepan over medium heat; cook and stir until warmed through, 3 to 5 minutes. Add water if mixture seems too thick. Pour over raisin mixture in the bowl and mix with your hands until combined.
Line a square baking dish with parchment paper. Press mixture into the baking dish. Brush remaining banana puree on top. Cover with plastic wrap.
Chill until firm, 8 hours to overnight. Cut into squares.