From the sources
(א:כט Bereishit) ” וַיְבָ֣רֶךְ אֹתָם֮ אֱלֹהִים֒ וַיֹּ֨אמֶר לָהֶ֜ם אֱלֹהִ֗ים פְּר֥וּ וּרְב֛וּ וּמִלְא֥וּ אֶת־הָאָ֖רֶץ וְכִבְשֻׁ֑הָ וּרְד֞וּ בִּדְגַ֤ת הַיָּם֙ וּבְע֣וֹף הַשָּׁמַ֔יִם וּבְכָל־חַיָּ֖ה הָֽרֹמֶ֥שֶׂת עַל־הָאָֽרֶץ׃ וַיֹּ֣אמֶר אֱלֹהִ֗ים הִנֵּה֩ נָתַ֨תִּי לָכֶ֜ם אֶת־כָּל־עֵ֣שֶׂב ׀ זֹרֵ֣עַ זֶ֗רַע אֲשֶׁר֙ עַל־פְּנֵ֣י כָל־הָאָ֔רֶץ וְאֶת־כָּל־הָעֵ֛ץ אֲשֶׁר־בּ֥וֹ פְרִי־עֵ֖ץ זֹרֵ֣עַ זָ֑רַע לָכֶ֥ם יִֽהְיֶ֖ה לְאָכְלָֽה׃”
“God blessed them and God said to them, “Be fertile and increase, fill the earth and master it; and rule the fish of the sea, the birds of the sky, and all the living things that creep on earth.” God said, “See, I give you every seed-bearing plant that is upon all the earth, and every tree that has seed-bearing fruit; they shall be yours for food.”” (Bereishit 1:28-29)
Adam HaRishon is told that he can eat any vegetables, grasses or fruits, but not meat. Sanhedrin 59b states that birds and fish were included in this prohibition. For more information see http://www.yeshiva.co/ask/?id=97, which discusses the Talmud’s view on what Adam HaRishon was allowed to eat at this time.
How to eat it
This could be a week to make a vegetarian Shabbat. You could make a big salad containing fruit, vegetables, “grass” (alfalfa sprouts or wheatgrass) and seeds to represent all of the foods that WERE permitted to Adam HaRishon.
