(def pie-chart
    ^{:portal.viewer/default :portal.viewer/vega-lite}
    {:description
     "A simple pie chart with labels."
     :data
     {:values
      [{:category "a", :value 4}
       {:category "b", :value 6}
       {:category "c", :value 10}
       {:category "d", :value 3}
       {:category "e", :value 7}
       {:category "f", :value 8}]}
     :encoding
     {:theta
      {:field "value"
       :type "quantitative"
       :stack true}
      :color
      {:field "category"
       :type "nominal"
       :legend nil}}
     :layer
     [{:mark {:type "arc", :outerRadius 80}}
      {:mark {:type "text", :radius 90}
       :encoding
       {:text
        {:field "category", :type "nominal"}}}]
     :view {:stroke nil}})

I'm not too familiar with the vega-lite DSL, sorry