Preheat the oven to 400 degrees F. Crumble the tuna into a mixing bowl. Add the onions, eggs, garlic, and relish. Mix thoroughly. Season the mixture with salt and pepper. Stir in enough mayonnaise to moisten the salad according to taste. Reseason the salad with salt and pepper. Spread a quarter of the salad over four pieces of bread and place on a baking sheet. Top each salad with a piece of cheese. Place the sheet in the oven and cook for a couple of minutes or until the cheese melts. Season the tomato slices with salt and pepper. Peel and remove the pit from the avocado. Slice the avocado into 1/4-inch slices. Season the avocado with salt and pepper. Top the melted cheese with the tomatoes, avocados and remaining slices to toasted bread. Place each sandwich on a plate and cut in half. Garnish the sandwiches with the Cole slaw, chips, and pickles.