mensa/src/components/Mensa.vue

<template>
  <div class="hello">
    <router-link :to="'/' + $route.params.mensa + '/heute'">Heute</router-link>
    <router-link :to="'/' + $route.params.mensa + '/morgen'">Morgen</router-link>
    <router-link :to="'/' + $route.params.mensa + '/uebermorgen'">Übermorgen</router-link>
    <p>{{$route.params.mensa}}</p>
    <router-view></router-view>
  </div>
</template>

<script>
export default {
  name: 'mensa',
  data () {
    return {
    }
  },
  created () {
    if (!this.$route.params.tag) {
      this.$router.replace(`heute`)
    }
  }
}
</script>

<!-- Add "scoped" attribute to limit CSS to this component only -->
<style scoped>
h1, h2 {
  font-weight: normal;
}

ul {
  list-style-type: none;
  padding: 0;
}

li {
  display: inline-block;
  margin: 0 10px;
}

a {
  color: #42b983;
}
</style>