tabsetgetyoucrazy.R

library(shiny)

ui <- fluidPage(
  fluidRow(
    column(width = 12,
           tabsetPanel(
             tabItem("main", "MENU"),
             tabItem("more", uiOutput("hello"))
           ))
  )
)

server <- function(input, output, session) {
  output$hello <- renderUI({
    list(
      tabsetPanel(
        tabItem("main", "MENU"),
        tabItem("more", "ok")
      )
    )
  })
}

shinyApp(ui, server)