Place eggplant on paper towels; cover with 1 teaspoon salt. Let sit until moisture is drawn out, 10 to 30 minutes.
Preheat oven to 350 degrees F (175 degrees C). Heat canola oil in a deep fry pan over medium heat.
Heat olive oil in a skillet over medium heat; add the leek. Cook and stir until leek is slightly translucent, about 5 minutes. Stir in spinach; cook until slightly wilted, 3 to 5 minutes. Add garlic; cook and stir until spinach is fully wilted, about 3 minutes. Remove from heat.
Combine panko, Parmesan cheese, and parsley in a bowl. Whisk flour, paprika, salt, and pepper together in a separate bowl; pour in beer. Whisk until batter is loose, adding more beer if batter is too thick. Dredge eggplant in the batter, allowing excess to run off; coat in panko mixture.
Drop 1 pinch of panko into the canola oil to test the heat. It should bubble up without splattering out. Fry battered eggplant for 30 seconds; flip. Fry until golden brown, about 30 seconds. Place on a paper towel to drain.
Combine spinach mixture, ricotta cheese, salt, and pepper in a bowl; spread an even amount onto 4 of the fried eggplant slices. Sprinkle with mozzarella cheese; cover with a second slice of fried eggplant. Top with mozzarella cheese. Place onto a baking sheet.
Bake in the preheated oven until cheese is golden brown, about 10 minutes.
