Preparation Place quartered kumquats in processor; puree 3 minutes. Measure 1/3 cup puree for glaze; set aside. Position rack in center of oven; preheat to 350°F. Spray two 8 1/2x4 1/2x2 1/2-inch metal loaf pans with nonstick spray. Combine flour, tea powder (if desired), baking powder, baking soda, cardamom, and 1 1/2 teaspoons salt in medium bowl; whisk to blend. Using electric mixer, blend 1 1/4 cups sugar and oil in large bowl. Beat in eggs, 1 at a time, then vanilla, 2/3 cup kumquat puree, and pineapple with juice. Gradually add dry ingredients, beating just until blended. Fold in walnuts. Divide batter between prepared pans. Bake cakes until tester inserted into center comes out clean, about 1 hour. Cool 5 minutes in pans on rack. Turn cakes out; place top side up on rack and cool. Place reserved 1/3 cup puree in large bowl. Whisk in butter, powdered sugar, lemon juice, and 1/2 teaspoon salt. Spread glaze over cakes, dividing equally. Top with kumquat slices. Let stand until icing sets. (Can be made 1 day ahead. Wrap in foil; store at room temperature.)
Preparation Place quartered kumquats in processor; puree 3 minutes. Measure 1/3 cup puree for glaze; set aside. Position rack in center of oven; preheat to 350°F. Spray two 8 1/2x4 1/2x2 1/2-inch metal loaf pans with nonstick spray. Combine flour, tea powder (if desired), baking powder, baking soda, cardamom, and 1 1/2 teaspoons salt in medium bowl; whisk to blend. Using electric mixer, blend 1 1/4 cups sugar and oil in large bowl. Beat in eggs, 1 at a time, then vanilla, 2/3 cup kumquat puree, and pineapple with juice. Gradually add dry ingredients, beating just until blended. Fold in walnuts. Divide batter between prepared pans. Bake cakes until tester inserted into center comes out clean, about 1 hour. Cool 5 minutes in pans on rack. Turn cakes out; place top side up on rack and cool. Place reserved 1/3 cup puree in large bowl. Whisk in butter, powdered sugar, lemon juice, and 1/2 teaspoon salt. Spread glaze over cakes, dividing equally. Top with kumquat slices. Let stand until icing sets. (Can be made 1 day ahead. Wrap in foil; store at room temperature.)