I was born in Slovenia but we made mostly Italian sweets. My cousin made the most delicious apple strudel with chocolate and apples and nuts. Peanut butter is not on their menu so that the Slovenian cake would not have it in it.
Per Wikipedia, it contains poppy seeds, walnuts, apples, raisins and ricotta fillings. You can find a recipe for it at slovenia dot info - just search the site for "gibanica" - it's in English.