Season the slider patties with adobo seasoning and oregano on both sides.
Heat a skillet over medium-high heat and cook the patties for about 3–4 minutes per side, or until fully cooked. Set aside.
Cut off the ends of the green plantains. Score the skin lengthwise and peel.
Slice each plantain into 4-5 equal pieces.
Heat about 2 inches of vegetable oil in a skillet over medium-high heat.
Fry the plantain pieces for approximately 1½ minutes per side until lightly golden.
Remove the plantains and flatten each piece using a tostonera, plate, or the bottom of a cup.
Return the flattened plantains to the hot oil and fry a second time until golden brown and crispy, about 2-3 minutes per side.
Remove and drain on paper towels.
In a small bowl, combine the mayonnaise, ketchup, and minced garlic. Mix until smooth.
To assemble, spread mayo ketchup on both sides of two plantain pieces.
Add cheese (if using), a cooked slider patty, lettuce, and tomato.
Top with another plantain piece and serve immediately with sliced avocado on the side.