Preheat oven to 350 degrees F (175 degrees C). Spread walnuts on a baking sheet.

Toast walnuts in the preheated oven until fragrant, about 5 minutes.

Combine toasted walnuts and oats in a food processor; grind into a fine meal. Mix with melted butter in a bowl. Mix in brown rice flour, 1/4 cup sugar, and 1 teaspoon salt. Press mixture into an 8-inch glass baking dish to form crust.

Bake crust in the preheated oven until edges start to brown, about 30 minutes. Let cool, about 10 minutes. Spread raspberry preserves on top.

Beat cream cheese and 1/2 cup sugar in a bowl with an electric mixer until smooth. Beat in eggs, maple syrup, lemon zest, and 1/2 teaspoon salt. Spread cream cheese mixture evenly over the raspberry preserves.

Bake in the preheated oven until the edges start to brown and the center is mostly set, about 45 minutes.

Cool cheesecake to room temperature, at least 2 hours. Refrigerate until firm, 8 hours to overnight. Cut into squares.