In a saucepan over medium heat, add the diced apples and butter. Let it cook until the apples are just tender. It will take about 6 - 7 minutes. Stir occasionally.
In a small mixing bowl, add in the brown sugar, cinnamon, and cornstarch. Whisk until combined.
Add the sugar mixture in with the apples once they are tender. Whisk to combined. Let the mixture come to a boil and let it boil until it thickens about 1 minute. Remove from the heat and let cool.
While the apple filling is cooling, prepare the crisp topping.
In a medium bowl, add the cold butter, brown sugar, flour and oats. Using two forks or a pastry cutter, cut the butter in until it's pea sized.
Lay your egg roll wrapper flat.
Fill a small bowl with 3 T of water. Dip your finger in the water and and run it around all sides of the wrapper.
Add about 2 T. of apple filling and 2 T. crisp topping to the wrapper. I normally run it in a straight line from one corner to the other leaving an inch and half from the corners for folding. You can put a little more or a little less depend on how full your wrapper is. You don't want to overfill them and have them explode in the hot oil.
Start at the corner in the middle of the filling and pull it over the filling and tuck it in. Add a little water to the two corners that are on either side of the filling. Place them on top of the wrapper. These will become the ends. Roll the filling tight and be sure the last corner sticks down. If it doesn't add a small amount of water and press it down. It should seal. Repeat with the other 5 egg rolls.
Add the vegetable oil to large saucepan. Let it heat to 375. Use a candy thermometer to keep track of the temperature.
Add 2 egg rolls at a time. Let them cook about 3 minutes on either side or until golden brown. Remove from the oil and place on a plate lined with paper towels. Repeat with the over 4 egg rolls. Serve while warm.